EP0078719B1 - Self-blast switch with permanent magnet - Google Patents

Description

• - une enveloppe étanche remplie d'un gaz à rigidité diélectrique élevée,
• - une chambre divisionnaire à l'intérieur de ladite enveloppe,
• - une paire de contacts logés dans ladite chambre divisionnaire et ayant des électrodes annulaires de contact formant des pistes de rotation dudit arc,
• - un logement, ménagé à l'intérieur de l'un des contacts, dans lequel est logé un aimant permanent annulaire dont la face frontale est coiffée par l'une associée desdites électrodes annulaires, de façon que l'aimant engendre un soufflage magnétique en rotation de l'arc ancré sur ladite électrode annulaire associée,
• - un conduit d'échappement du gaz de ladite chambre divisionnaire s'étendant à travers l'orifice central de l'aimant annulaire et de l'électrode annulaire associée.

The invention relates to a rotary arc and self-expanding switch comprising:

• - a sealed envelope filled with a gas with high dielectric strength,
• - a divisional chamber inside said envelope,
• a pair of contacts housed in said divisional chamber and having annular contact electrodes forming tracks of rotation of said arc,
• - A housing, arranged inside one of the contacts, in which is housed an annular permanent magnet whose front face is capped by one associated with said annular electrodes, so that the magnet generates a magnetic blowing in rotation of the arc anchored on said associated annular electrode,
• - A gas exhaust duct from said divisional chamber extending through the central orifice of the annular magnet and the associated annular electrode.

The document FR-A-2 480 028 relates to a switch of the kind mentioned comprising either a permanent magnet having on the front face a blind orifice, or an annular permanent magnet polarized radially. The permanent magnet with blind recess does not allow a double blowing of the arc which limits the performances of this switch to a cut of the currents lower than approximately 10000 Amperes. The annular magnet allows gas to escape through the central duct and a double blowing of the arc, but the performance of this switch has been found to be relatively limited to a value close to that of the permanent magnet with blind orifice. The present invention starts from the observation that the annular permanent magnet does not always provide effective rotation blowing of the root of the arc, the latter tending to stagnate on the contacts. Further study has shown a partial closure of the lines of force of the magnetic field on the front face of the permanent magnet which creates areas of axial field towards which the arc tends to move. In these axial field areas the arc is not subjected to any rotational force and the switch behaves like a simple autoexpansion switch.

The object of the present invention is to remedy these drawbacks and to allow the production of a permanent magnet arc blowing switch having performances comparable to those of arc blowing coil switches.

The switch according to the invention is characterized in that said magnet is axially polarized to generate in the area, adjacent to the associated annular electrode, on the one hand a radial magnetic field oriented in the central part in one direction and in the external part in the opposite direction, and on the other hand an axial magnetic field at the cusp points separating said central and external parts, and that the annular electrode opposite to said associated electrode is arranged so that the arc extends between said annular electrodes in said central part of the magnetic field, said switch comprising means for transferring outwards from said front face said cusps and avoiding any displacement of the arc towards said cusps.

The magnetic field generated by an axially polarized annular permanent magnet is shown in axial section in FIG. 1 and it can be seen that the lines of force close symmetrically inside and outside the permanent magnet. In the example shown in FIG. 1, the force lines are centripetal in the central part of the permanent magnet and centrifugal towards the outside and an area with axial force lines separates the centrifugal and centripetal force lines. The cusp corresponding to the axial force lines is arranged substantially in the middle of the pole face of the permanent magnet and it is understood that the arc tends to move towards this zone with magnetic blowing in zero rotation. According to the present invention, the cusp is moved outward from the pole face in an area inaccessible to the arc.

In a first embodiment of the invention, the displacement of the turning point towards the outside of the permanent magnet is carried out by a yoke in the form of a tubular ferrule extending in the orifice of the annular magnet . The tubular yoke distorts the magnetic spectrum by moving the cusp outward from the permanent magnet. It will appear from the following description that the presence of the magnetic yoke creates a second magnetic field zone with a significant axial component in line with the end face of the yoke, but in this zone the pneumatic blowing is maximum and the extinction of the arc is made quickly.

According to a second embodiment of the invention, the external diameter of the permanent magnet is significantly enlarged, so as to move the turning point away from the internal orifice of the magnet.

The contact opposite to the permanent magnet is advantageously of tubular shape to constitute a second gas exhaust duct and a double blowing of the arc, the diameter of the tubular part corresponding substantially to the diameter of the internal orifice of the permanent annular magnet. It is clear that the opposite contact can also include a permanent annular blowing magnet, the assembly being in this case entirely symmetrical.

• la figure 1 est une vue schématique en coupe axiale, montrant le spectre d'un champ magnétique engendré par un aimant permanent annulaire, dans un interrupteur ne donnant pas satisfaction ;
• la figure 2 est une vue schématique en coupe axiale, illustrant un interrupteur selon l'invention, en positions fermé et ouvert, respectivement sur les demi-vues de gauche et de droite ;
• la figure 3 est une vue simplifiée d'une variante de réalisation, selon l'invention, montrant les électrodes et l'aimant annulaire.

The current is supplied to the annular electrode covering the annular permanent magnet takes place from the outside of the magnet in order to avoid on the one hand any demagnetization of the permanent magnet in the manner described in the aforementioned French document, and with a view, on the other hand, to generating a centering effect of the arc by looping effect. Other advantages and characteristics will emerge more clearly from the description which follows of different embodiments of the invention, given by way of nonlimiting examples and represented in the appended drawing, in which:

• Figure 1 is a schematic view in axial section, showing the spectrum of a magnetic field generated by an annular permanent magnet, in an unsatisfactory switch;
• Figure 2 is a schematic view in axial section, illustrating a switch according to the invention, in closed and open positions, respectively on the left and right half-views;
• Figure 3 is a simplified view of an alternative embodiment, according to the invention, showing the electrodes and the annular magnet.

In FIG. 1, a permanent magnet 10 of annular shape is axially polarized, the polar face, for example of north polarity, being covered with an annular contact electrode 12. Opposite the annular electrode 12 is arranged an annular electrode 14 formed by the front face of a tubular contact piece 16. The diameter of the tubular piece 16 is substantially equivalent to the diameter of the internal orifice 18 of the permanent magnet 10 disposed coaxially with the tubular piece 16. The lines of force are schematically represented in FIG. 1 and include centripetal radial lines 20 and centrifugal radial lines 22 in the intermediate zone between the electrodes 12, 14. The centripetal radial lines 20 and centrifugal 22 are separated symmetrically by an area of axial lines 2.4 corresponding to a cusp 26 of the pole face of the permanent magnet 10. the assembly is symmetrical and the cusp _'26 or more e xactively the cusps 26 are arranged on a circle equidistant from the internal and external circles of the annular magnet 10.

An arc extending between the electrodes 12 and 14 tends to move towards the cusp 26 and this arc shown at 28 in Figure 1 stagnates in this position, the magnetic field exerting no rotational force. It is clear that a switch incorporating such a device has performance and therefore very limited interest.

2 shows an improved switch using the basic elements shown in Figure 1, which can be recognized, in particular the permanent annular magnet 10, the electrode 12 covering the front face of the annular magnet 10, the part tubular 16 with its front face 14 opposite the annular face 12. The tubular part 16 is slidably mounted to come either into contact with the annular electrode 12 in the closed position of the switch, or in a spacing position, shown on the right side of Figure 2, in the open position. The permanent magnet assembly 10, annular electrodes 12, 14, is housed inside a chamber 30, constituted for example by a cylindrical envelope 32, itself housed in an enclosure 34, filled with a gas with rigidity high dielectric, in particular of sulfur hexafluoride. The movable tubular part 16 crosses the bottom of the chamber 30 and communicates through a lateral orifice 36 with the enclosure 34, so as to create a gas exhaust duct from the chamber 30 to the enclosure 34. The annular electrode 12, associated with the permanent magnet 10, is electrically connected to a cylindrical conductor 38 externally surrounding the annular permanent magnet 10 and connected to a support and current supply tube 40 passing through the bottom of the chamber 30 and communicating by an orifice 42 with the enclosure 34. It is easy to see that the tubular support 40 defines a second conduit 44 for exhausting gases from the chamber 30 to the enclosure 34, through the magnet 10 and the annular electrode 12. The support assembly 40, permanent magnet 10 and associated annular electrode 12, is mounted fixed, the arc being drawn between the electrodes 12, 14 when sliding down the tubular part 16. The arc s extends into the chamber 30 and in a manner known per se causes by heating an increase in the pressure in this chamber 30 and an escape of the gases through the exhaust conduits 36, 44 in the movable contact 16 and in the assembly constituting the fixed contact, in this case the annular electrode 12 and the support 40. The permanent magnet is axially polarized, for example making a north pole face appear opposite the opposite annular electrode 14 carried by the tubular part 16. A magnetic yoke 46 has a cylindrical ferrule 48 extending in the orifice 18 of the permanent magnet 10 while being attached to the internal periphery of this magnet 10 and by being flush with the front face of the magnet 10. The yoke 46 further comprises an annular disc 50 connecting to the internal ferrule 48 and attached to the polar posterior face of the permanent magnet 10. The yoke 46 modifies the magnetic spectrum of the permanent magnet 10, represented on the right part of FIG. 2, by creating an asymmetry and an offset towards the outside of the permanent magnet 10 of the cusp 52. The centrifugal force lines 54 bypass the permanent magnet from the outside while the centripetal force lines 56 are concentrated towards the end of the ferrule 48.

• En position fermée de l'interrupteur, représentée sur la partie gauche de la figure 2, le courant, passant par le contact mobile 16, les électrodes aboutées 14, 12, le conducteur cylindrique 38 et le support 40, n'exerce aucune force de désaimantation sur l'aimant permanent 10. Il convient de préciser que la culasse 46 est avantageusement isolée des pièces conductrices du courant ou est agencée pour offrir une résistance notable au passage du courant. En position d'ouverture, représentée sur la partie droite de la figure 2, l'arc s'étendant entre les électrodes 12, 14 peut être considéré comme un nuage conducteur intercalé entre les électrodes 12, 14. Ce nuage conducteur comporte trois parties essentielles, en l'occurrence une partie centrale soumise à l'action du champ magnétique centripète radial 56, une partie externe tendant à se déplacer vers le point de rebroussement 52 et une partie interne ancrée sur le bord interne de l'électrode annulaire 12. Cette dernière partie s'étend dans une zone de champ axial, mais elle est soumise à un soufflage pneumatique intense dû à l'échappement des gaz à travers le conduit d'échappement 44 favorisant une extinction rapide. La partie centrale est soumise à un soufflage magnétique dû à la composante radiale importante 56 du champ engendré par l'aimant permanent 10. La partie externe est soumise à une force de centrage s'opposant au déplacement vers le point de rebroussement 52, d'une part due à l'effet de soufflage par les gaz s'échappant par les conduits d'échappement, et d'autre part par les forces électrodynamiques ou effets de boucle résultant de l'amenée de courant par le pourtour externe de l'électrode annulaire 12. L'interrupteur est capable de couper de larges gammes de courant et son pouvoir de coupure est élevé. La figure 2 représente le mode de mise en oeuvre préférentiel selon l'invention, et il est à noter que le dispositif de soufflage par aimant permanent annulaire à aimantation axiale peut être utilisé en combinaison avec un contact opposé plein en faisant appel à un soufflage unique. D'une manière analogue, il est possible de prévoir deux aimants permanents annulaires agencés symétriquement et chacun étant associé à l'un des contacts tubulaires. La culasse 46 ne comporte pas obligatoirement un disque postérieur 50, seule la concentration des lignes de force dans la zone frontale étant importante. Le dispositif de soufflage selon l'invention peut être utilisé en combinaison avec d'autres contacts susceptibles de transférer l'arc sur les électrodes annulaires 12, 14. La forme et la disposition de la culasse 46 peut être différente et le déplacement du point de rebroussement 52 vers une zone éloignée de l'électrode annulaire opposée 14 peut être réalisé d'une manière différente par exemple illustrée par la figure 3.

The switch according to FIG. 2 operates as follows:

• In the closed position of the switch, represented on the left part of FIG. 2, the current, passing through the movable contact 16, the butted electrodes 14, 12, the cylindrical conductor 38 and the support 40, exerts no force of demagnetization on the permanent magnet 10. It should be noted that the yoke 46 is advantageously isolated from the conductive parts of the current or is arranged to offer significant resistance to the passage of current. In the open position, represented on the right part of FIG. 2, the arc extending between the electrodes 12, 14 can be considered as a conductive cloud interposed between the electrodes 12, 14. This conductive cloud comprises three essential parts, in this case a central part subjected to the action of the radial centripetal magnetic field 56, an external part tending to move towards the cusp 52 and an internal part anchored on the internal edge of the annular electrode 12. This last part extends in an axial field zone, but it is subjected to an intense pneumatic blowing due to the escape of gases through the exhaust duct 44 promoting rapid extinction. The central part is subjected to a magnetic blowing due to the large radial component 56 of the field generated by the permanent magnet 10. The external part is subjected to a centering force opposing the movement towards the cusp 52, on the one hand due to the blowing effect by the gases escaping through the exhaust ducts, and on the other hand by the electrodynamic forces or loop effects resulting from the supply of current by the external periphery of the electrode annular 12. The switch is capable of cutting wide ranges of current and its breaking capacity is high. FIG. 2 represents the preferred embodiment according to the invention, and it should be noted that the blowing device by annular permanent magnet with axial magnetization can be used in combination with a full opposite contact by using a single blowing . Similarly, it is possible to provide two annular permanent magnets arranged symmetrically and each being associated with one of the tubular contacts. The cylinder head 46 does not necessarily have a rear disc 50, only the concentration of the lines of force in the frontal area being important. The blowing device according to the invention can be used in combination with other contacts capable of transferring the arc to the annular electrodes 12, 14. The shape and the arrangement of the yoke 46 may be different and the displacement of the point of cusp 52 towards a zone remote from the opposite annular electrode 14 can be produced in a different way, for example illustrated by FIG. 3.

In Figure 3 are shown only the elements of the switch arranged inside the chamber 30, and we recognize the movable part 16 with the annular front surface 14 disposed in front of the fixed part with support 40. The annular permanent magnet with axial polarization, represented by the reference 58, is a magnet similar to that bearing the reference 10 in FIG. 2, but with a significantly increased external diameter. An associated annular electrode 60 covers the pole face of the magnet 58 while being electrically connected to the support 40 by conductive parts 62 surrounding the permanent magnet 58 externally. As indicated above, the gases compressed by heating in the chamber 30 can escape through the exhaust duct 44 passing through the central hole of the annular magnet 58 and by the duct formed by the tubular part 16. The permanent magnet 58 does not have a yoke and the magnetic field is entirely symmetrical, in particular the turning point 64. The increase in the external diameter of the annular magnet 58 makes it possible to move the turning point 64 away from the annular electrode 14 , so as to avoid, in the manner described above, any displacement of the arc towards this cusp point 64. It is unnecessary to describe the operation of this variant embodiment which is exactly identical to that described in relation to the switch represented in FIG. 2. It is clear that the increase in the external diameter of the permanent magnet 58 can be combined with the action of a cylinder head for channeling the magnetic flux or any other means of modifying ication of the magnetic arc blowing spectrum. The offset towards the outside of the cusp point 64 is particularly visible by comparison with the device illustrated in FIG. 1. Good results have been obtained by increasing the diameter of the circle formed by the cusp points 64 to a substantially double value the diameter of the annular electrode 14.

The wall of the tubular part 16 is advantageously small in the two variants described above, so as to present an annular electrode 14 of small width exactly positioning the arc. The diameter of this annular electrode can of course be slightly different, in particular less than the diameter of the orifice formed in the annular permanent magnet 10, 58, in particular when the blowing effect through the tubular part 16 can be reduced.

Claims (9)

1. Self-blast switch with rotating arc comprising :

- a tight enclosure (10) filled with a gas of high dielectric strength,

- a divisional chamber (30) inside said enclosure,

- a pair of contacts located in said divisional chamber (30) and having ring-shaped contact electrodes (12, 14) constituting rotation tracks of said arc,

- a housing, located inside one of the contacts, in which is disposed a ring-shaped permanent magnet (10) the front side of which is covered by the associated one (12) of the ring-shaped electrodes so that the magnet (10) generates a magnetic blast rotation of the arc fastened on the said associated ring-shaped electrode (12),

- a gas exhaust conduct (44) of said divisional chamber (30) extending through the central opening (18) of the ring-shaped magnet (10) and of the associated ring-shaped electrode (12), characterized by the fact that said magnet (10) is polarized axially in order to produce in the area adjacent to the associated ring-shaped electrode (12) on the one hand a radial magnetic field directed in the central part in one direction (56) and in the external part in the opposite direction (54), and on the other hand an axial magnetic field at the return (52) which separate the central and external parts, and that the ring-shaped electrode (14) opposite to said associated electrode (12) is so arranged that the arc extends between said ring-shaped electrodes (12, 14) in said central part (56) of the magnetic field, said switch comprising means (46, 58) in order to transmit to said external front face said return points (52, 64) and to avoid any movement of the arc towards said return points (52, 64).

2. Switch according to claim 1, characterized in that it comprises with respect to the permanent magnet (10) an internal tube-shaped yoke (46) to generate an asymmetry of the magnetic field transmitting the return points (52) to the outside.

3. Switch according to claim 2, characterized in that the internal tube-shaped yoke (46) extends in the central opening (18) of the permanent magnet (10) and constitutes said exhaust conduct (44).

4. Switch according to claim 2 or 3, characterized in that the internal yoke (46) comprises in addition to the tube (48) a plate (50) covering the rear pole face of the magnet (10).

5. Switch according to one of the preceding claims, characterized in that said ring-shaped opposite electrode (14) is constituted by the end face of a tubular piece with a thin wall with a diameter quite equal to that of the central opening (18) of the permanent magnet (10).

6. Switch according to claim 5, characterized in that said tubular piece (16) constitutes a second gas exhaust conduct (36) of said divisional chamber (30) with a section near to that of said conduct (44).

7. Switch according to one of claims 5 or 6, in combination with one of the claims 2-4, characterized in that the internal yoke (46) is isolated electrically on the rear face of said contact (12) in order to impose a passage of the current at the outside of the permanent magnet (10) and a centering of the arc by loop effect of the current lines.

8. Switch according to one of the preceding claims, characterized in that the diameter of the circle formed by said return points (52, 64) is greater than the double of the diameter of said opposite ring-shaped electrode (14).

9. Switch according to one of the preceding claims, characterized in that a second permanent ring-shaped magnet (10, 58) is associated to the other of said contacts.

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